Why this book? Firstly, because the Spanish anarchist movement of the early 20th century was, without a doubt, the most powerful and influential anarchist movement on the planet and remains so even today. Secondly, because the Spanish anarchism that emerged before 1939 provided a very rich and innovative terrain for social and revolutionary experimentation. Indeed, it has been suggested that Spain developed the strongest and most creative working-class culture of any that materialised in interwar Europe. Thirdly, because given our current situation, in which words like eco-fascism and collapse are again becoming current, and it seems that libertarian ideas and practices are destined to resurface. This concise text offers a critical introduction to the Spanish anarchist movement. It surveys achievements, contradictions and shortcomings. It acknowledges controversies and sharp divergences of opinion and addresses often-neglected issues: self-management, decentralization, federalism, nationality, and the role of the State and of the bureaucracy. It includes a bibliography and a listing of documentaries and movies.